This invention relates to a light-sensitive member (particularly a light-sensitive member for electrophotography) and a method for preparing the same.
Generally speaking, a substance capable of generating a visible light absorbing carrier can be difficult to form into a film. Only a very few substances such as amorphous selenium are suitable, and may have the further drawback having poor retentive force for the charges given to its surface. On the contrary, a substance excellent in film-forming ability and capable of retaining charges of 500 V or higher for a long time with a thickness of about 10 .mu.m has generally the drawback of having no sufficient photoconductivity by absorption of a visible light.
For such reasons, it has been proposed to provide laminate of a carrier generating layer containing a substance capable of generating charged carriers by absorption of a visible light and a carrier transporting layer for transporting either one or both of the positive and negative charged carriers generated in the carrier generating layer and constituted the light-sensitive layer of such a laminate. Thus, by dividing the functions of generation and transportation of the charged carriers to be possessed separately by different substances, the scope for choice of materials can be broadened to improve various characteristics required in electrophotographic process, such as charge retentive force, surface strength, sensitivity to visible light and stability during repeated use.
As a method of preparing such a function-separation type 10. light-sensitive member, there are the method in which the carrier generating layer and the carrier transporting layer are formed by coating by using separate coating solutions, respectively, and the method in which the carrier generating layer is formed by vapor deposition. The carrier generating layer may include the case containing a resin and the case containing no resin, but improvement of sensitivity is desired in either case.
Japanese Unexamined Patent Publication No. 55643/1977 discloses an example in which an amine is used as the solvent for the purpose of enhancing sensitivity of the light-sensitive member. According to this method, dye substances for generation of carriers soluble in an primary organic amine (azo type dye and squaric acid derivative) are dissolved in a solvent containing an organic primary amine, and the resultant solution is applied on an electroconductive substrate to form a carrier generating layer.
Whereas, as a result of the investigation made by the the present inventors on the technique for generating a carrier generating layer with an amine as the solvent as described above, the following defects were found to occur.
That is, because an amine type solvent is used as the coating solvent, the amine content in the coating solvent is required to be enough to dissolve completely the azo type dye, namely in an amount exceeding 20%. For this reason, the drying time after coating is prolonged and the coated product after drying is also inconvenient in handling on account of the sticky surface of the carrier generating layer, etc. Moreover, many organic amines have strong stimulating odors and therefore use of much amount of an amine will worsen the environmental conditions during coating. To be more important, the performance of an azo type dye is determined by its crystalline state, but the azo type dye becomes completely amorphous state because it is coated by dissolving according to such a method as described above, whereby no sufficient performance can be obtained. Also, because a large amount of amine is used by dissolution, the absorption wavelength of the carrier generating layer is shifted toward the shorter wavelength side to result in great lowering in photosensitivity or great lowering in dark decay or acceptive potential during repeated uses of the light-sensitive member.
The present inventor has found that the causes for the problems as mentioned above are too large amount of an amine contained in the carrier generating layer as well as the too high amine concentration in the coating solution, as the result of using a large amount of an amine for dissolving a carrier generating substance in the known technique of the prior art as described above.